Pyridinium salt-based covalent organic framework with well-defined nanochannels for efficient and selective capture...

Ionic covalent organic framework (COF) materials with high specific surface areas and well-defined pore structures are desired for many applications yet seldom reported. Herein, we report a cationic pyridinium salt-based COF (PS-COF-1) with a Brunauer-Emmett-Teller (BET) surface area of 2703 m² g^-1, state-of-the-art for an ionic COF. Aided by its ordered pore structure, chemical stability, and radiation resistance, PS-COF-1 showed exceptional adsorption properties toward aqueous ReO₄^- (1262 mg g^-1) and ⁹⁹TcO₄^-. Its adsorption performance surpassed its corresponding amorphous analogue. Importantly, PS-COF-1 exhibited fast adsorption kinetics, high adsorption capacities, and selectivity for ⁹⁹TcO₄^- and ReO₄^- at high ionic strengths, leading to the successful removal of ⁹⁹TcO₄^- under conditions relevant to low-activity waste streams at US legacy Hanford nuclear sites. In addition, PS-COF-1 can rapidly decontaminate ReO₄^-/⁹⁹TcO₄^- polluted potable water (∼10 ppb) to drinking water level (0 ppb, part per billion) within 10 min. Density functional theory (DFT) calculations revealed PS-COF-1 has a strong affinity for ReO₄^- and ⁹⁹TcO₄^-, thereby favoring adsorption of these low charge density anions over other common anions (e.g., Cl^-, NO₃^-, SO₄^2-, CO₃^2-). Our work demonstrates a novel cationic COF sorbent for selective radionuclide capture and legacy nuclear waste management.